Conformational Locking of the Geometry in Photoluminescent Cyclometalated N^C^N Ni(II) Complexes

Niazi M, Maisuls I, Mai L, Schäfer SA, Oster A, Santiago Diaz L, Guldi DM, Doltsinis NL, Strassert CA, Klein A (2025)

Publication Type: Journal article

Publication year: 2025

Journal

Molecules MDPI

Book Volume: 30

Article Number: 1901

Journal Issue: 9

DOI: 10.3390/molecules30091901

Abstract

In our research aimed at replacing precious transition metals like platinum with abundant base metals such as nickel for efficient triplet emitters, we synthesized and studied Ni(II) complexes [Ni(L^NHR)Cl]. These complexes containing the N^C^N cyclometalating dipyridyl-phenide ligand, equipped with pending H-bonding amine groups (NH(C₆H₅) (L^NHPh) and NH(C₆H₅CH₂), ClL^NHBn). Molecular structures determined from experimental X-ray diffractometry and density functional theory (DFT) calculations in the ground state showed marked deviation of the Cl⁻ coligand (ancillary ligand) from the ideal planar coordination, with τ4 values of 0.35 and 0.33, respectively, along with hydrogen bonding interactions of the ligand NH function with the Cl⁻ coligand. The complexes exhibit long-wavelength absorption bands at approximately 425 nm in solution, with the experimental spectra being accurately reproduced through time-dependent density functional theory (TD-DFT) calculations. Vibrationally structured emission profiles and steady-state photoluminescence quantum yields of 30% for [Ni(L^NHPh)Cl] and 40% for [Ni(L^NHBn)Cl] (along with dual excited state lifetimes in the ns and in the ms range) were found in frozen 2-methyl-tetrahydrofuran (2MeTHF) glassy matrices at 77 K. Furthermore, within a poly(methyl methacrylate) matrix, the complexes showed emission bands centered at around 550 nm within a temperature range from 6 K to 300 K with lifetimes similar to 77 K. Based on TD-DFT potential scans along the metal–ligand (Ni–N) coordinate, we found that in a rigid environment that restricts the geometry to the Franck-Condon region, either the triplet T5 or the singlet S4 state could contribute to the photoluminescence.

Authors with CRIS profile

Lukas Mai Lehrstuhl für Physikalische Chemie I Lukas Santiago Diaz Lehrstuhl für Physikalische Chemie I Dirk Michael Guldi Lehrstuhl für Physikalische Chemie I

Involved external institutions

Universität zu Köln

Germany (DE) Westfälische Wilhelms-Universität (WWU) Münster

Germany (DE)

How to cite

APA:

Niazi, M., Maisuls, I., Mai, L., Schäfer, S.A., Oster, A., Santiago Diaz, L.,... Klein, A. (2025). Conformational Locking of the Geometry in Photoluminescent Cyclometalated N^C^N Ni(II) Complexes. Molecules, 30(9). https://doi.org/10.3390/molecules30091901

MLA:

Niazi, Maryam, et al. "Conformational Locking of the Geometry in Photoluminescent Cyclometalated N^C^N Ni(II) Complexes." Molecules 30.9 (2025).

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